The present invention relates to male fastener components that engage in openings of a female component, in particular to loops formed by fibers of a nonwoven female component. The invention more particularly relates to stem and head formations of the male elements that promote loop engageability and to methods and machines for their manufacture, and their use. In other aspects the invention relates to manufacture of male fastener members per se, with application for instance to so-called self-engaging fasteners as well as to hook and loop fasteners. The invention in some respects, also relates to specific products of which the following is one example.
Attachment strips for window screens have been formed of, among other things, the male component of a hook and loop type fastener. To secure the screen, the male fastener elements are inserted through the openings of the mesh material and engage the sides of the mesh openings. It is desirable that the engagement between the male fastener elements and the mesh openings provide good peel strength, so that the screen is not detached by wind, and that the attachment strip be inexpensive and relatively attractive.
There is a general need for male fastener components for hook and loop fasteners that provide good peel and shear strength properties in desired single or multiple directions that are relatively inexpensive to manufacture, and a specific need for male fastener components that can function with low cost nonwoven loop materials.
There is also a need to be able to produce male fastener products having differing functional characteristics consistently and efficiently, using techniques that require limited changeover in basic tooling, yet allow for adjustments to produce the desired fastener characteristics.
Furthermore, it is especially desirable to extend the use of hook and loop fastening systems into fields of low cost products and still obtain good fastening performance. Examples include mid- and lowest-cost disposable diapers and sanitary products, disposable packaging for low price products, and disposable lowest cost surgical and industrial clothing and wraps. There are many other recognized low-cost product areas to which such fasteners would be applicable.
In particular it is desirable to obtain good engagement of the male member of the fastening system with low cost nonwoven loop products, which are characterized by their thinness and the low height to which their loop-defining fibers extend.
“Good engagement” in some instances means engaging a large percentage of hooks with low-lying loops.
“Good engagement” in other applications often requires more, as in the case of fasteners for diapers. In such instances the hook component must exhibit strong “peel” resistance when engaged with thin, low cost loop materials. With such materials, effective loop height does not permit transition of loading from the hook head to the hook stem during peeling action, as does occur with expensive loop products that have higher loop height. For this reason there are special problems to be addressed with hooks for thin loop structures in addition to the need to reduce the cost of the hook component.
To explain the peel considerations more fully, in a hook and loop type fastener, “peel strength” is the resistance to stripping of one component from the other when a force normal to their mating surfaces is applied to the extremity of one of the components. Such peeling force on the component causes it to flex and progressively peel from the other. It is desirable to have such peel strength in a hook and loop fastener that ensures that the closure does not release under normal forces of use but still permits the components to be separated when required.
When the loop element is thin, as is usually the case for low-cost female fasteners, the structure of individual loops is very short and low-lying. In this condition, with application of a peel force, the loop exerts a force on the hook, which is essentially perpendicular to the sheet-form base and parallel to the stem of the individual hooks. Consequently the force is applied only to the heads of the hooks.
In contrast, when the loop element has a thick pile structure comprised of long individual loops, a loop must first be pulled out to its full length before it can exert a significant force on a hook. As this occurs, the base webs to which the hooks and loops are attached are enabled to flex away from each other (see FIG. 23Y) so that at the point of separation of hooks from such loops, the mated components are no longer face to face. Therefore the angle at which a loop exerts its force on a hook is less than perpendicular. The longer the loop length, the more that angle diminishes. As a result, with a long loop component, the force not only acts on the head of the hook, but also on its stem. For very long loops, most of the resistance force is on the stem during peeling action.
The consequence is that for short loops, the hook head must be strong and provide much of the resistance to peel separation, while for long loops, a short rigid stem with a slight head overhang is sufficient to give high resistance to peel separation. Therefore, in many instances, in order to expand and improve the use of thin and inexpensive loop components, the hook head geometry must be improved to increase strength of engagement and produce an acceptable closure.
In many cases it is desirable to form the male hook members for use with short loop material by molding an array of stems integrally (i.e. monolithically) with a common base, and subsequently to post-treat the stems by a pressed formation step to form loop-engageable heads. In many instances it is desired to use continuous processes that act in a given machine direction, but to find a way to do this so as to achieve a hook product that has good peel strength characteristics when the user applies peel forces at a substantial angle to the machine direction, and in many cases at right angles, e.g., in the cross-machine direction.